Photocatalytic Carbon Dioxide Reduction and Density Functional Theory Investigation of 2,6-(Pyridin-2-yl)-1,3,5-triazine-2,4-diamine and Its Cobalt and Nickel Complexes

Carbon dioxide (CO2) is an important trace
gas in Earth’s
atmosphere. Its high concentration in the environment causes serious
problems. Thus, it has become imperative to develop efficient ways
to reduce CO2. One of the best strategies to transform
this greenhouse gas is the use of solar energy for the photochemical
reduction of CO2. However, this process is challenging
due to a number of drawbacks that should be overcome for it to become
a promising alternative for generation of sustainable fuels and chemicals.
In this work, we have engineered molecular photocatalysts based on
2,6-(Pyridin-2-yl)-1,3,5-triazine-2,4-diamine 1 which
mimic [2,2′;6′,2′′]terpyridine (tpy) and its related complexes by coordination with transition
metal ions. Because of the functional groups (-NH2 group)
and the electronic structural modification of 1 as compared
with tpy, remarkable photocatalytic properties over the
CO2 reduction to CO were found for the free and metal ligands
with turnover numbers (TONs) between 80–102 with BIH and 480–1370
with BID. An integrated method using structural characterization by
X-ray diffraction analysis, experimental and density functional theory
calculations was used to track the mechanistic pathways of the photocatalytic
CO2 reduction reaction.